The ability to image within a living body is fundamental to the proper diagnosis and treatment of medical conditions. Typically, a medical device such as a catheter or endoscope is used to gain access to and image remote regions of the body otherwise reachable only with invasive surgery. These systems use a variety of imaging techniques such as acoustical and optical imaging.
Acoustical imaging systems generally place either a phased array or single rotating transducer at the distal end of the medical device. The transducer emits acoustic pulses, i.e., mechanical sound waves, and receives the acoustic reflections that are created by the impact of these pulses with the surrounding tissues. The acoustic imaging system can then generate an image of the internal tissue based on the information provided by these reflections. The acoustic imaging system is able to produce images despite the presence of blood or other fluids surrounding the tissue. This makes acoustic imaging ideal for applications which require scanning large regions of internal tissue. For instance, when scanning internal body lumens such as blood vessels, the acoustic system can image the vessel both radially around the vessel circumference as well as longitudinally along the length of the vessel, typically referred to as “pull back.” Scanning of large regions within the blood vessel can take place without seriously impeding the flow of blood.
Optical imaging systems are similar to acoustic systems in that they typically include an optical imager at the distal end of the medical device. However, optical imaging systems use the transmission and receipt of optical energy, e.g., light, to create images of tissue within the body. Optical imaging systems typically employ a type of optical coherence domain reflectometry (OCDR), such as optical coherence tomography (OCT), to generate high quality images of internal tissue. Optical imaging systems are typically faster than acoustic imaging systems and can provide a higher degree of resolution. However, because optical imaging is dependent on the propagation of light, the presence of fluids or materials that impede light propagation can prevent proper imaging. For instance, when an optical imaging system is used to image the interior of a blood vessel, the flow of blood through that vessel must be sequestered, either by introducing saline to dilate the blood within the vessel or by stopping the flow of blood altogether. Sequestration for extended periods of time, in some case for less than sixty seconds, starves the tissue of oxygen and can result in serious adverse effects and is not desired. Because optical systems require obstruction of blood flow, they can only scan for limited periods of time and accordingly, optical imaging systems are not suited for scanning large regions of tissue in a safe manner.
Thus, there is a need for improved systems and methods of imaging internal tissue.